Acrylic graft polymers have been known for use in the coatings industry as binders for thermosetting compositions. Acrylic graft polymer binders typically have a plurality of functional sites reactive with the functional sites of one or more crosslinking agents and upon cure, produce hard, durable, glossy films suitable for use in a variety of coating applications. Preferred applications include automotive primers, basecoats, and clearcoats. Such coatings may be waterborne, solventborne, powder, or combinations thereof.
The manufacture of acrylic graft polymers has typically involved the production of an acrylic backbone polymer having one or more functional sites per molecule. At least one of these functional sites must be capable of subsequent or concurrent reaction with at least one functional group of a graft moiety.
Graft copolymerization processes have traditionally been used to incorporate moieties that cannot be incorporated via the free radical polymerization of the acrylic backbone. Examples of such moieties include polymers such as polyesters, polyurethanes and the like, surfactants, halogenated compounds, certain water dispersible groups, especially nonionic groups, and simple alkyl groups.
However, numerous problems occur during such prior art graft copolymerization processes. In particular, in the processes of the prior art, the reaction of the graft moiety and the acrylic backbone polymer results in reaction products which are reactive with one or more species, including the acrylic backbone functionality, other intermediate species, and/or the graft moiety. Such undesirable side reactions result in uncontrolled molecular weight growth, the loss of desired functionality, and/or gellation.
In addition, the uncontrollable reactivity of the functional group used as the grafting site on the acrylic backbone limits the use of additional functionality on the acrylic backbone and hinders the production of multifunctional acrylic backbone polymers. As a result, it has been difficult to obtain certain multifunctional graft copolymers using the processes of the prior art.
For example, if an epoxy group is used as the grafting site on the acrylic backbone, ethylenically unsaturated monomers having functional groups reactive with epoxy must be avoided during the polymerization of the acrylic backbone if the epoxy group results from the use of an ethylenically unsaturated monomer such as glycidyl methacrylate. Illustrative functional groups that would have to be avoided include active hydrogen containing groups such as amine functional ethylenically unsaturated monomers, acid functional ethylenically unsaturated monomers, and depending, on the polymerization conditions, hydroxy containing ethylenically unsaturated monomers.
Assuming that the acrylic backbone polymer's functionality is limited to epoxy groups, the use of amine, hydroxy, or acid functional graft moieties will result in a variety of intermediate species which are reactive with the graft moiety, the epoxy functionality of the acrylic backbone or both. As a result, attempts to use an amine or acid functional graft moiety will often lead to uncontrolled molecular weight growth, the loss of desired functionality on the backbone, and/or gellation.
It would thus be advantageous to provide a method of graft polymerization that would address the deficiencies of the prior art. In particular, what is desired is a method of graft polymerization that would facilitate the production of multifunctional graft acrylic polymers, especially multifunctional graft polymers wherein at least one functional group of the acrylic backbone polymer is hydroxyl. Such improved acrylic graft polymer manufacturing processes would have a decreased risk of uncontrolled molecular weight growth, the loss of desired acrylic backbone functionality, and/or gellation.
It is thus an object of the invention to provide a method of making multifunctional graft acrylic polymers and copolymers that eliminates the disadvantages of the prior art.
In particular, it is an object of the invention to provide a method of obtaining an acrylic graft polymer having at least two functional groups that would be reactive with each other under polymerization conditions. That is, the at least two functional groups would react with each other if incorporated via the free radical polymerization of at least two ethylenically unsaturated monomers having such functional groups.
It is another object of the invention to provide a method of making a urethanized acrylic graft polymer having at least one hydroxyl group.
Finally, it is an object of the invention to provide a method of making a urethanized acrylic graft polymer having at least one hydroxyl group and at least one functional group which is not hydroxyl and would be reactive with a hydroxyl group under free radical polymerization reaction conditions.